A common desire in the field of semiconductor integrated circuits is the provision of thin film electrical resistors on an individual integrated circuit chip or on a substrate to be associated with one or more of such chips. Typically such resistors are formed by providing a uniform thin film over all or a substantial portion of the surface on which the resistors are desired. A photoresist material is then coated over the thin film. The photoresist is exposed and developed, leaving a coating of photoresist over those portions of the thin film which are to be retained, but no resist covering those portions of the film to be removed.
The film is then subjected to an etching process. The regions of the film covered by the resist material are protected from etching and thus retained on the surface, while those portions unprotected by the resist are removed. The resist layer may then be removed, leaving the completed electrically resistive structures.
The etching step of the above description could involve any of a number of different etching processes. For example, it could be a plasma etch or a wet chemical etch. In a wet chemical etch the assembly including the film to be etched is placed in a solution including the etchant.
Thin film resistors of the type described are sometimes formed of a combination of chromium and silicon. Wet chemical etching of the chromium silicon resistors has often been performed by using a combination of HF, HCl, and H.sub.2 O. Recently, the inclusion of nitrogen in the chromium silicon mixture has been found to improve the performance of the electrical resistors formed. Unfortunately the films containing chromium, silicon, and nitrogen cannot effectively be etched using the above etchant. Therefore, if wet chemical etching of such resistive films is to be performed a different etchant must be identified.